Filter device

ABSTRACT

A filter device for transmission oil, having a filter element ( 24 ) which can be inserted into a transmission oil pan ( 70 ) and the filter medium ( 32 ) of which separates an unfiltered side from a filtrate chamber, which is connected in a fluid-conveying manner to an outlet ( 38, 50, 72 ), to which a negative-pressure device such as a suction oil pump, can be connected, wherein the filter medium ( 32 ) of the filter element ( 24 ) has at least one structural layer ( 46 ) having a predetermined surface area and predeterminable filter properties and having at least one further structural layer ( 44, 60 ) having predeterminable filter properties, wherein the surface area of the further structural layer ( 44; 60 ) is different from the surface area of the first structural layer ( 46 ), and wherein the respective structural layers ( 44, 46, 60 ) encompass an inner filter cavity ( 30 ), is characterized in that the respective structural layers ( 44, 46, 60 ) are pleated having the same type of pleats, in that the pleated structural layers ( 44, 46, 60 ) [extend] in axial alignment between two end caps ( 22, 34 ) of the filter element ( 24 ), [and in that,] viewed in the flow direction of the fluid flow to be cleaned, the respective structural layers ( 44, 60 ) having the higher filtration grade are downstream of an upstream structural layer ( 46 ) each having a lower filtration grade.

The invention relates to a filter device for transmission oil, having a filter element, which can be inserted into a transmission oil pan and whose filter medium separates an unfiltered side from a filtrate chamber, which is connected to an outlet in a fluid-conveying manner, to which a negative pressure conveying device, such as an oil suction pump, can be connected, wherein the filter medium of the filter element has at least one structural layer having a predetermined surface area and having predetermined filter properties and at least one further structural layer having predetermined filter properties, wherein the surface area of the further structural layer differs from the surface area of the first structural layer, and wherein the individual structural layers comprise an internal filter cavity.

To ensure the safe and trouble-free operation of transmissions over long operating periods, it is state of the art to provide a filter device for the transmission oil, cf. DE 10 2007 023 641 B4, in which a filter device of the aforementioned type, which operates as a suction filter, is disclosed. The design as a suction filter is characterized by significantly smaller installation space requirements compared to a pressure oil filter device, i.e., unlike pressure oil filter devices, which normally operate in a bypass flow and are mounted inside the transmission housing or on the outside of the transmission housing, they can be installed without difficulty directly in the oil sump of the oil pan of the individual transmission. For optimum maintenance of the transmission oil, it is advantageous to provide filter media having different filter properties for the filtering process, through which the unfiltered medium can flow. The well-known filter device mentioned above provides for two filter media in the form of a coarse filter medium and a fine filter medium, each formed by a flat filter, which are arranged one above the other inside the oil pan.

Based on this state of the art, the invention addresses the problem of providing a filter device of the type mentioned at the outset, which permits filtering a flow passing filter media having different filter properties and which is characterized by a particularly space-saving design.

According to the invention, this object is achieved by a filter device that has the features of claim 1 in its entirety.

According to the characterizing part of patent claim 1, the invention provides as a solution of this problem that the individual structural layers are pleated having the same type of pleats, that the pleated structural layers extend axially aligned between two end caps of the filter element and that, viewed in the direction of flow of the fluid flow to be cleaned, a structural layer having a higher filtration grade is downstream of a preceding structural having a lower filtration grade. By combining structural layers having different filter properties into a single filter medium instead of the separate, superimposed filter media provided by the state of the art mentioned above, a compact design can be achieved which requires little installation space and is therefore particularly suitable for installation in the oil pan of a transmission housing. Because, further according to the invention, the individual structural layers also have different surface areas, i.e. partial flows of the suction flow flow through the structural layers having different properties, a simple parallel arrangement of the differently filtered parts of the suction flow is achieved.

For this purpose, the filter medium is designed such as described in DE 10 2004 061 078 A1 for a filter component, in which a first structural layer is designed in the manner of a main filter and a further structural layer is designed in the manner of a prefilter. As explained in this document, the prefilter layer extends as a first structural layer having a predeterminable surface area and having a predeterminable length in the form of a longitudinal strip, wherein a further second structural layer in the form of a main filter having a predeterminable length, which is smaller than the length of the prefilter, is arranged on the top of the structural layer.

In accordance with the known filter component mentioned above, the filter medium has structural layers having different filtration grades.

The structural layers can be pleated in the manner typical for filter mats, preferably having the same type and number of pleats, wherein the structural layers can be single-layer or multi-layered.

The pleated structural layers are arranged as a filter mat between end caps and encompass an inner filter cavity. In this way an easily usable and, if necessary, exchangeable unit is created, which constitutes a standardized filter element, which constitutes a cost-effective solution for the transmission oil system.

If the fluid flows through filter mat of the filter element from the inside to the outside, wherein the inner filter cavity as the unfiltered side is connected to the oil sump of the assigned oil pan in a fluid conveying manner, the filter mat can have a supporting structure on the outside encompassing the outer structural layers. If the fluid flows through the filter mat of the filter element from the outside to the inside, wherein the inner filter cavity forms the filtrate side, the filter mat may have an inner supporting structure in contact with the inner structural layer.

In particularly advantageous exemplary embodiments, a filter element in the form of a flat filter is provided, whose filter mat, which encompasses the filter cavity, has a flat cross-sectional shape having large-area plane long sides and narrow, rounded short sides in relation to a section plane extending in parallel to the end caps, wherein one long side of the filter element faces the bottom of the assigned transmission oil pan. Such exemplary embodiments are characterized by a particularly low overall height and thus require little installation space.

The arrangement can advantageously be such that the filter element in the oil pan is accommodated in an inner housing, which has an inlet, routed to the inner filter cavity, the filtrate chamber encompassing the filter element and a fluid outlet routed to a suction port.

The fluid inlet may be formed by an opening in the bottom of the inner housing.

Alternatively, the fluid inlet can be formed by a flat tubing routed to the oil sump of the oil pan, which is arranged on a side wall of the housing or inner housing and with which a connecting piece of the filter element engages, which connecting piece is arranged eccentrically on the facing end cap of the filter element and forms the connection to the filter cavity.

For the connection of the filtrate chamber of the inner housing to a suction port, the arrangement may be advantageously such that the fluid outlet of the inner housing is formed by a hollow housing part located next to the flat tubing on the side wall of the inner housing, which forms a passage between the filtrate chamber of the inner housing encompassing the filter element and the suction port.

For the flow through the filter mat from the outside to the inside, the arrangement may be particularly advantageous in that the filter element in the oil pan is arranged in an inner housing, which is open to the oil sump, encompasses a rectangular receiving space for the filter element having long sides and short sides and has an end wall extending along one short side, wherein the suction port is located in the end wall, with which a connecting piece is engaged, which at one end cap of the filter element forms a passage to the filter cavity and thus a support part for one end of the filter element.

In this arrangement, the end cap at the other end of the filter element can form a protruding foot part, which forms a support part at the bottom of the oil pan for one end of the filter element.

Below the invention is explained in detail with reference to exemplary embodiments shown in the drawing. In the Figures:

FIG. 1 shows a perspective oblique view of the first exemplary embodiment of the design of the filter device according to the invention, wherein the housing is cut away near the upper part having a horizontal section plane and shown with the side wall of the housing cut away in parts;

FIG. 2 shows a perspective oblique view of the exemplary embodiment, wherein the housing is cut away in a vertical angular section and the filter element is shown without the upper end cap;

FIG. 3 shows an angular section similar to FIG. 2, wherein the filter element is shown having an upper end cap and having a support tube encompassing the filter medium on the outside;

FIG. 4 shows a perspective oblique view of a second exemplary embodiment, wherein the upper housing cover is omitted;

FIG. 5 shows a vertical section of the exemplary embodiment of FIG. 4;

FIG. 6 shows a vertically section perspective oblique view of the exemplary embodiment of FIGS. 4 and 5, wherein an outer support tube of the filter medium is only shown in part;

FIG. 7 shows a vertical section of a third exemplary embodiment of the invention of a filter device installed in an oil pan, of which only part is shown broken off;

FIG. 8 shows a perspective oblique view of a fourth exemplary embodiment of the design of the invention filter device having an inner housing, which can be installed in an oil pan and which is shown without a cover part;

FIG. 9 shows a schematically simplified vertical section of the exemplary embodiment of FIG. 8;

FIG. 10 shows a perspective oblique view of the exemplary embodiment of FIGS. 8 and 9, wherein parts of the inner housing are cut away; and

FIG. 11 shows a perspective oblique view similar to FIG. 10, wherein the filter element is partially cut away.

The first exemplary embodiment shown in FIGS. 1 to 3 shows a housing 2 in the form of a hood, which has a square outline having rounded corner areas 4, a flat upper cover 6 and flat side walls 8 extending vertically downwards therefrom. At the lower end 10, the side walls 8 merge into a horizontal, flat end rim 12, which encompasses the entire open lower end of the hood. As FIGS. 2 and 3 show, the underside of the end rim 12 forms the contact surface for a ring body 14 and a peripheral edge 16 of a base plate 18. The peripheral edge 16 adjoins a wall part 20 of the base plate 18, which extends obliquely upwards from the plane of the base plate 18 such that the housing 2 having the end rim 12 resting on the peripheral edge 16 is raised on spacers at a distance from the main plane of the base plate 18.

The ring body 14 is part of a lower end cap 22 of the filter element 24 that is inserted into the housing 2. Due to the contact of the annular body 14 with the end rim 12, which is at a distance from the base plate 18, a free space is formed between the filter element 24 and the base plate 18, which free space forms a filter operation of the chamber holding the unfiltered medium 26, into which the unfiltered medium flows via a fluid inlet 28 formed in the base plate 18. In the case of an injection-molded housing 2 made of a plastic material such as PA6 and an end cap 22 made of plastic, the connection of the annular body 14 of the filter element 24 inserted into the housing 2 can be made by welding or gluing before the connection with the peripheral edge 16 of the base plate 18 is formed. If the housing parts are made of metallic material, these joints may also be formed by gluing or welding.

As FIGS. 2 and 3 show, the lower end cap 22 is open to the inner filter cavity 30 encompassed by the hollow cylindrical filter mat 32, whereas the upper end cap 34 of the filter element 24 closes the filter cavity 30 at the upper end. If the suction flow direction is from the inner filter cavity 30 to the outside, the outside of the filter element 24 in housing 2 forms a filtrate chamber 36, from which the filtrate exits via a suction port 38, which is formed at a corner area 4 in the area of cover 6. To keep the base plate 18 at a distance from the base of the assigned oil pan (not shown), 18 spacers 40 are formed on the underside of the base plate, of which only one is visible in FIGS. 2 and 3.

Each filter element 24 of the solution presented here has two end caps 22, 34 at the ends, forming an insertable unit, but these are not always shown in the figures for the sake of a clear illustration, or only partly in the form of showing only one end cap 22 or 34.

The spacers 40 safeguard an unobstructed flow from the oil sump to the inner filter cavity 30 during suction filter operation. The structural layers of the filter mat 32 are supported against the suction flow running from the inside to the outside by a support tube 42 shown only in FIG. 3, which extends on the outside of the pleated filter mat from the lower end plate 22 to the upper end plate 34. In the exemplary embodiment shown, one of the structural layers of the multilayer filter mat 32 has a surface area that differs from the other structural layers. In the example shown, this is the structural layer designated by 44, which, starting from the upper end cap 34, extends as an outer layer over approximately half the axial length of the filter mat 32 and thus over half the length of the other structural layers 46. As shown, the structural layer 44 is folded into the pleated composite of the filter mat 32. The structural layer 44 forms a filter area for the suction flow, the filtration grade of which differs from the filtration grade of the adjacent area of the filter mat 32. During suction filtering, parallel suction flow sections are therefore formed in which, for instance, pre-filtration and fine filtration are performed simultaneously next to each other.

FIGS. 4 to 6 show a second exemplary embodiment, in which a filter element 24 in the form of a flat filter is provided, in which the filter mat 32 does not form a hollow circular cylinder but has a flat cross-sectional shape in relation to a section plane extending in parallel to the end caps 22. As shown in these figures, the outside of the filter mat 32 therefore has flat, large-surface long sides 52 and 54 (cf. FIG. 5) and narrow, rounded flat sides 56 and 58 (cf. FIG. 6). As in the first exemplary embodiment, the pleated filter mat 32 has an outer structural layer 60, which has a filtration grade and surface area different from that of the other structural layers 46. In contrast to the first exemplary embodiment, this additional structural layer 60 is not connected to an end cap 22, but is arranged in the central area of the axial length of the filter mat 32 and ends equidistantly in front of the adjacent end cap 22, which distances are approximately one quarter of the total axial length of the filter mat 32.

As in the first exemplary embodiment, the housing 2 is formed by a hood, the cover 6 of which is omitted in FIG. 4 and which has a low overall height to adapt to the flat shape of the filter element 24. As in the first exemplary embodiment, the flat housing 2 is mounted on a base plate 18, which has a wall part 20 extending upwards along its circumferential area, as in the first exemplary embodiment, and on the circumferential edge 16 of which the lower end rim 12 of the housing 2 rests. In contrast to the first exemplary embodiment, no opening is provided on the base plate 18 for the inflow from the oil sump, but a flat tubing 62 is located on one side wall 8 of the housing, which, cf. FIG. 4, is arranged off-center on the side wall 8.

As FIG. 5 shows, the filter element 24 has a connecting piece 64 at its end cap 22, which is eccentric at the end cap 22 and engages with the flat tubing 62. The connecting piece 64, sealed by means of a sealing ring 66, establishes the connection between the oil sump and the inner filter cavity 30 of the filter element 24 for the suction filter process via the flat tubing 62 forming the fluid inlet. A fluid outlet 50, which is only shown in FIG. 5, used to discharge the suction flow from the filtrate chamber 36 encompassing the filter element 24 is formed on cover 6 of housing 2. As in the first exemplary embodiment, the outside of the filter mat 32 is supported against the suction flow running from the inside to the outside by means of a support tube 42.

FIG. 7 shows a third exemplary embodiment, in which the filter element 24, which is designed as a flat filter like in the second exemplary embodiment, is received in an inner housing 68 installed in a transmission oil pan 70. In the same way as in the first exemplary embodiment, the filter mat 32 of the filter element 24 has a structural layer 44, which differs from the other structural layers 46 in terms of filtration grade and surface area, which extends, like in the first exemplary embodiment, from the end cap 34 approximately along half the axial length of the filter mat 32. For the fluid inlet, the inner housing 68 has the same flat tubing 62 as is provided eccentrically on the side wall 8 of the housing 2 there in the second exemplary embodiment, cf. FIG. 4. As in the second exemplary embodiment, the end cap 22 of the filter element 24 also has a connecting piece 64 engaging with the flat tubing 62, which forms the connection to the inner filter cavity. For the efflux from the filtrate chamber 36 encompassing the filter mat 32, the inner housing 68 has a fluid outlet which is formed by a hollow housing part 72 which, in addition to the flat tubing 62 which is arranged eccentrically on the side wall 8 of the inner housing 68, forms a fluid passage via which the suction flow from the filtrate chamber 36 is guided via the hollow housing part 72 to the suction port 38, which in this exemplary embodiment is located in a port chamber 74 formed in the oil sump 70.

FIGS. 8 to 11 show a fourth exemplary embodiment of a filter device according to the invention, in which the filter element 24 is arranged in an inner housing 80 to be installed in a transmission oil pan. In this exemplary embodiment, the flow is directed from the outside through the filter mat 32 extending between the end caps 22 and 34 to the inner filter cavity 30 during the filtering process. Accordingly, as shown most clearly in FIG. 9, a pipe socket 92 is formed on one end cap 22, which pipe socket establishes a connection with the inner filter cavity 30 via a passage 82 in the end cap 22, which inner filter cavity forms the filtrate side.

In the installed state of the inner housing 80, the connecting piece 92 engages with the suction port 38, which in this exemplary embodiment is located on an end wall 90 of the inner housing 80, which end wall forms a support part of the inner housing 80, which can be used to immobilize the inner housing 80 in the relevant oil pan.

As FIGS. 8 and 10 show, the end wall 90 has the shape of a square plate, which at a short side 86, cf. FIG. 8, delimits a receiving space 84 having a rectangular outline for the filter element 24, from which short side longitudinal sides 88 extend in vertical planes towards the opposite short side 86. The longitudinal sides 88 are not full-surface wall parts but have recesses 98, like the short side 86 opposite the end wall 90, i.e. the receiving space 84 in the inner housing 80, which is closed on the top by a flat cover part 100 omitted in FIG. 8, is open towards the oil sump.

The end cap 34 of the filter element 24, which is opposite from the end cap 22 having the passage 82, forms a flat closing plate of the hollow body formed by the filter mat 32. In contrast to the exemplary embodiment of FIG. 1, it is not a round body but, as in the exemplary embodiments of FIGS. 4 to FIG. 7, has a non-circular shape, wherein the cross-sectional shape in the exemplary embodiment in FIGS. 8 to 11 corresponds to a square having rounded corner areas. The end cap 34 has a corresponding shape, apart from a foot part 94, which protrudes downwards in the form of a flat strip such that, when installed in a transmission oil pan, it stands on the base of the oil pan and thus forms a supporting part for one end of the filter element 24, the other end of which is fixed to the end wall 90 via the connecting piece 92 located at the end cap 22, which in turn forms a supporting part of the inner housing 80.

A prefilter formed of the individual superimposed structural layers can be designed in terms of fluid permeability such that it permits high fluid quantities to pass through at an acceptable dirt holding capacity, which is improved by a higher filtration grade of the main filter, formed by a further structural layer, with the result that the fluid permeability of the prefilter is reduced to a minimum during a so-called cold start of the engine when the transmission oil to be filtered is still cold and correspondingly highly viscous, the flow resistance of the prefilter is low and the main filter in conjunction with parts of the prefilter then provides the desired dirt pick-up capacity.

Several structural layers having different filter properties and different areas of the superimposed layers can be combined, resulting in a variety of design options for the individual filter element. For instance, very high separation rates (beta values) at different differential pressures of the fluid to be filtered or the filtration of certain fluid components of a fluid to be filtered, which can only be detected from a certain structural position, can be implemented. The filter element can be individually adapted to the individual transmission situation functions by replacing and using structural layers in a self-explanatory manner when creating a new filter element in the way of a kind of modular system, which is without parallel in the prior art. It is particularly advantageous to select the respective overlap in such a way that the edge of a structural layer placed on another structural layer is equidistant to both longitudinal sides of the other structural layer, which improves the fluid flow behavior of the filter element. It is irrelevant whether the fine filter layer forming the main filter is adjacent to one of the end caps or at a distance from both end caps. 

1. A filter device for transmission oil, having a filter element (24), which can be inserted into a transmission oil pan (70) and whose filter medium (32) separates an unfiltered side from a filtrate chamber, which is connected in a fluid-conveying manner to an outlet (38, 50, 72), to which a negative-pressure device such as a suction oil pump, can be connected, wherein the filter medium (32) of the filter element (24) has at least one structural layer (46) having a predetermined surface area and predeterminable filter properties and having at least one further structural layer (44, 60) having predeterminable filter properties, wherein the surface area of the further structural layer (44; 60) is different from the surface area of the first structural layer (46), and wherein the respective structural layers (44, 46, 60) encompass an inner filter cavity (30), characterized in that the respective structural layers (44, 46, 60) are pleated having the same type of pleats, in that the pleated structural layers (44, 46, 60) extend in axial alignment between two end caps (22, 34) of the filter element (24), and in that, viewed in the flow direction of the fluid flow to be cleaned, the respective structural layers (44, 60) having the higher filtration grade is downstream of an upstream structural layer (46) each having a lower filtration grade.
 2. The filter device according to claim 1, characterized in that the structural layers (44, 46, 60) are single-layer or multi-layered.
 3. The filter device according to claim 1, characterized in that, in order to flow through the filter mat (32) from the inside to the outside, the inner filter cavity (30) is connected the oil sump of the assigned oil pan (70) as an unfiltered side in a fluid conveying manner, and in that the filter mat (32) has a supporting structure (42) on the outside encompassing the respective outer structural layers (44, 46, 60).
 4. The filter device according to claim 1, characterized in that, when the suction flow passes through the filter mat (32) from the outside to the inside, wherein the inner filter cavity (30) forms the filtrate side, the filter mat (32) has an inner supporting structure (96), which bears against the inner structural layers (44, 46, 60).
 5. The filter device according to claim 1, characterized in that a filter element (24) in the form of a flat filter is provided, whose filter mat (32), which encompasses the filter cavity (30), has a flat cross-sectional shape having large-area plane long sides (52, 54) and narrow, rounded short sides (56, 58) in relation to a section plane extending in parallel to the end caps (22, 34), and that one long side (54) of the filter element (24) faces the bottom of the assigned transmission oil pan (70).
 6. The filter device according to claim 1, characterized in that the filter element (24) in the oil pan (70) is accommodated in an inner housing (68), which has an inlet (62) routed to the inner filter cavity (30), the filtrate chamber (36) encompassing the filter element (24) and a fluid outlet (72) routed to a suction port.
 7. The filter device according to claim 1, characterized in that the fluid inlet is formed by an opening (28) in the bottom (18) of the housing (2).
 8. The filter device according to claim 1, characterized in that the fluid inlet is formed by a flat tubing (62) routed to the oil sump of the oil pan (70), which is arranged on a side wall (8) of the housing (2) or inner housing (68) and with which a connecting piece (64) of the filter element (24) engages, which connecting piece is arranged eccentrically on the facing end cap (22) of the filter element (24) and which forms the connection to the filter cavity (30).
 9. The filter device according to claim 1, characterized in that the fluid outlet of the inner housing (68) is formed by a housing part (72) located next to the flat tubing (62) at the side wall (8) of the inner housing (68), which housing part forms a passage between the filtrate chamber (36) of the inner housing (68) encompassing the filter element (24) and the suction port (38).
 10. The filter device according to claim 1, characterized in that for the flow through the filter mat (32) from the outside to the inside, the filter element (24) in the oil pan (70) is arranged in an inner housing (80), which is open towards the oil sump, encompasses a rectangular receiving space (84) for the filter element (24) having longitudinal sides (88) and short sides (86) and has an end wall (90) extending along one short side (86), and that the suction port (38) is located at this end wall, with which suction port a connecting piece (92) is engaged, which at one end cap (22) of the filter element (24) forms a passage (82) to the filter cavity (30) and thus a support part for one end of the filter element (24).
 11. The filter device according to claim 1, characterized in that the end cap (34) at the other end of the filter element (24) forms a protruding foot part (94), which forms a support part of one end of the filter element (24) at the bottom of the oil pan (70). 